1. Field
The present disclosure generally relates to acoustic treatments for controlling sound and noise, and deals more particularly with an acoustic panel fused for sound attenuation.
2. Background
High bypass type aircraft engines produce noise due to the high airflows through inlets, rotating stages and exhaust nozzles of the engines. In order to reduce noise and satisfy noise regulations governing commercial aircraft, high bypass engines may incorporate acoustic panels in various parts of the engine, such as in the inlets of engine nacelles. These acoustic panels, sometimes referred to as acoustic treatments or acoustic liners, may comprise a septumized honeycomb core sandwiched between a perforated inner skin and a non-perforated outer skin. The placement of septums in the cells of the honeycomb core form cavities that act as Helmholtz resonators which attenuate the sound/noise caused by high speed airflow into the inlets of the engine nacelles. Sound entering the cells of the core is dampened by the septum and reflected by the outer skin to partially cancel the incoming sound over a range of frequencies.
In some acoustic panels, only a septum in the core is used to dampen incoming acoustic waves, but the use of only a septum may limit the ability of the core materials to attenuate acoustic waves over a wide range of frequencies. Moreover acoustic cores that employ individual septums in core cells are time-consuming and expensive to fabricate. In other known acoustic panels, a layer of acoustic material is placed on one side of the inner skin which acts as an impedance to reduce the amplitude of acoustic waves entering the core, however the layer of acoustic material may provide acoustic wave attenuation over only a relatively narrow range of frequencies.
Accordingly, there is a need for an acoustic panel that is relatively economical to fabricate and which linearly attenuates undesired sound over a relatively wide range of frequencies.